NXP-2 association with SUMO-2 depends on lysines required for transcriptional repression.

Small ubiquitin-like modifier (SUMO) modification of transcription factors is generally associated with repression. Reverse genetic analysis of SUMO-1, and -2 conserved residues emphasized the importance of dual charge reversals in abrogating the critical role of SUMO-2 K33, K35, and K42 in repression. GST-SUMO-2-affinity chromatography followed by liquid chromatography (LC)-MS analysis identified proteins that appeared to bind preferentially to WT SUMO-2 versus SUMO-2 K33E and K35E. LSD1, NXP-2, KIAA0809 (ARIP4), SAE2, RanGAP1, PELP1, and SETDB1 bound to SUMO-2 and not to SUMO-2 K33E, K42E, or K35E and K42E. Although LSD1 is a histone lysine demethylase, and histone H3K4 was demethylated at a SUMO-2-repressed promoter, neither overexpression of a dominant-negative LSD1 nor LSD1 depletion with RNA interference affected SUMO-2-mediated repression, indicating that LSD1 is not essential for repression, in this context. When tethered to a promoter by fusion to Gal4, NXP-2 repressed transcription, consistent with a role for NXP-2 in SUMO-mediated repression. SUMO-2-associated proteins identified in this study may contribute to SUMO-dependent regulation of transcription or other processes.